The quantity of starch is at its maximum in the winter months, but as soon as the potato begins to sprout, the starch lessens, as does also the proportion of nitrogen,so that its nutritive properties are impaired. If, however, the process of isolating the starch be followed in the winter months, the result is, a sixth portion of the weight of the potatoes employed, in a condition fit not only for immediate use, but of easy transport, and capable of preservation for years.
Starches differ, according to their sources, in chemical composition, and certainly in their digestibility, as also in their nutritive properties, according as they are isolated or associated with other principles, such as gluten. Wheat-starch consists of while potato-starch consists of Arrowroot has no gluten associated with it, rice very little, potato only one-third what good wheat has. Thus while arrowroot is the most digestible, wheat is the most nourishing. Potatoes are neither nourishing nor digestible, being of all starches the most prone to run into acidity, and so distress weak stomachs. The consumers of rice and potatoes are remarked to be almost invariably pot-bellied, owing to the large quantity they are compelled to use. "To supply a given amount of carbon and nitrogen to the system it costs two and a half times as much to obtain it from potato as from bread." (Dr. Edward Smith.) These facts constitute a strong objection to the use of potatoes, either in their natural state, as when used at dinner, or when employed as a constituent of bread. Many persons have found their health strikingly improved by relinquishing the use of potatoes. It is difficult to detect the presence of potato-starch in
bread. The motive for using it is that it takes up more water than wheat-flour. But this is a double disadvantage to the consumer, as he gets leas nutritious material for his money, and has unhealthy acid generated in his stomach. The bread made with flour very moist is always inferior, from an alteration in the gluten, unfavourable to a perfect panification, and because such bread Is very much more prone to become mouldy, by which Its degree of wholesomeness is still farther impaired. (Dumas, ' Traiti do Chiral° appliqud aux Arta,' vol. vi. p. 391.) The carefully devised and systematically conducted experiments of Dr. Edward Smith prove that "animals cannot live on starch, and yet it is not uncommon to find mothers with deficient milk giving to their infants arrowroot, or some of the fashionable preparations of corn, which consist almost entirely of starch freed from the important nitrogenous constituents, and using water instead of cow's milk, under the impression that the latter would be too rich a food. Such a course can only be a source of starvation," and a fertile source of mortality. (See Practical Deductions from an Experimental Inquiry into the Influence of Foods,' by Edward Smith, M.D., Dublin, 1860.) The above are the more important kinds of starch. For information concerning starch from other sources see the names of the several plants In the NATURAL HISTORY Divislos of this Cyclopiedia. [An ROW ROOT ; SA00; SALE!'; TAPIOCA.'